Integration of cryogenic energy storage and cryogenic organic cycle to geothermal power plants

Abstract

To get more out of geothermal power generation, integration of energy storage technologies to geothermal power plants could be used for base load peak shaving operations. Cryogenic energy storage is one the attractive options to store geothermal power during off-peak hours and produce power during peak hours. In this study, a new configuration consisting of a binary geothermal power plant, an air liquefaction unit, and a cryogenic organic Rankine cycle is considered and analyzed using the first and second laws of thermodynamics.A geothermal resource available at 180 °C with a flow rate of 100 kg/s is used to power a binary cycle power plant with isopentane as the working fluid. Binary power plant produces 6253 kW power, which is used to liquefy air during a 6-h charging operation. During discharge operation, the liquefied air is pumped, and used as a heat sink for the cryogenic organic Rankine cycle with propane as the working fluid. The cryogenic organic Rankine cycle produces 1387 kW power. The liquid air after condensing operation is heated in the heaters with stored heat during charging operations and expanded in turbines for additional power generation. During the discharge operation, 10,660 kW power is produced by the combined cryogenic energy storage and cryogenic organic Rankine cycle unit while the total power generation is 16,920 kW. The cryogenic organic Rankine cycle system has a thermal efficiency of 35.3 % and a second law efficiency of 29.2 %. The storage system has a round-trip efficiency of 28.4 % and a second law efficiency of 59.7 %. Six different working fluids are analyzed and compared for the cryogenic organic Rankine cycle. Effects of condensing temperature and compressor outlet pressure of the cryogenic organic Rankine cycle, and geothermal resource temperature on the system performance are investigated.